NUCULANA. 193 



Nuculana ?, Meek and Worthen, 1866. Geol. Surv. Illinois, vol. ii, p. 283. 

 Toldia, Meek and Worthen, 1866. Ibid., p. 282. 



Leda, Young and Armstrong, 1871. Trans. Geol. Soc. Glasgow, vol. iii, Appendix, 



p. 51 ; and 1876, Cat. Carb. Foss. West. 

 Scotl., p. 54. 

 Toldia, Meek, 1872. U. S. Geol. Surv., Final Eeport Nebraska, p. 205. 

 Nuculana, Meek, 1872. Ibid., p. 206. 

 , Leda, B. Etheridge, jun., 1873. Mem. Geol. Surv. Scotland, Expl. Sheet 23, 



pp. 57, 64, &c. 

 — — 1873. Geol. Mag., vol. x, p. 347. 



Toldia, Meek, 1875. Eep. Geol. Surv. Ohio, vol. ii, pt. 2, p. 335. 

 Leda, B. Etheridge, jun., 1876. Ann. Mag. Nat. Hist., ser. iv, vol. xviii, p. 100. 

 Nucula, B. Etheridge, jun., 1876. Ibid., p. 104. 

 Leda, Boemer, 1876. Lethsea Geognostica, Atlas, pi. xliv, fig. 11. 

 Nuculana, B. Etheridge, jun., 1877. Quart. Journ. Geol. Soc, vol. xxxiv, p. 15. 

 — — 1878. Ann. Mag. Nat. Hist., ser. v, vol. ii, p. 33. 



Ctenodonta (pars), Bigsby, 1878. Thesaur. Devonico-Carboniferus, p. 303. 

 Nuculana (pars), Bigsby, 1878. Ibid., p. 310. 



— White, 1879. Bull. U.S. Geol. Surv. Territories, vol. v, No. 2, p. 216. 

 Aeca (pars), von Koenen, 1879. Neues Jahrbuch f. Min., &c, p. 336. 

 Nuculana, de Koninck, 1885. Ann. Musee E. H. N. Belgique, tome xi, p. 136. 



— (Leda), Etheridge, 1885. Brit. Foss., pt. 1, Palaeozoic, p. 288. 



— Keyes, 1888. Proc. Nat. Sci. Philadelphia, p. 233. 



— Waagen, 1888. Pal. Indica, set xiii, vol. i, Salt Eange Foss., p. 248. 

 Miller, 1889. N. American Geol. Palaeontol., p. 495. 



Nucula, Goodchild, 1892. Proc. Eoy. Phys. Soc. Edin., vol. xi, p. 244. 

 Nuculana, Keyes, 1894. Geol. Surv. Missouri, vol. v, pt. 2, p. 122. 

 Toldia, Keyes, 1894. Ibid., p. 123. 

 Nuculana, Tornquist, 1896. Fossil-furhend. Unter carbon Sudvogesen, p. 81. 



Generic Characters. — Shell transverse, more or less narrowed behind, and pro- 

 duced into a beak. Umbones small and contiguous, lunule and escutcheon well 

 marked. Cardinal border somewhat angular. Hinge-teeth in two sets, which 

 do not extend very far on each side of the umbo, numerous. A fossa for the 

 ligament, internal, placed between the anterior and posterior sets of teeth. 

 Posterior slope more or less keeled. Pallial line sinuated or not. Surface 

 ornamented with fine, regular, concentric, parallel grooves and lines. 



Observations. — The Carboniferous shells which I refer to the genus Nuculana 

 have been at times included in the genera Ctenodonta, Nucula, and Yoldia by 

 various authors. Although they do not possess a sinuated pallial line, and in this 

 respect agree with Nucula, yet the general shape, the attenuated and rostral form 

 of the posterior end, the possession of lunule and well-developed escutcheon, and 

 the concentric linear surface-markings are all important characteristics of the 

 genus Nuculana. It is interesting to note the absence of a sinuated pallial line in 

 shells which have so many characters in common with recent shells, but yet differ 



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